Gravity pouring molten metal into green sand or loose sand (e.g., the lost foam process) molds is a known technique for economically making metal castings. Highly sophisticated equipment for continuously pouring such molds is in commercial use. One such piece of equipment for casting molten iron is disclosed in Pol et al U.S. Pat. No. 3,977,461 which issued Aug. 31, 1976 and is assigned to the assignee of the present invention. Pol et al pours molten metal from a holding vessel into a series of sand molds moving through a pouring zone via a plurality of circulating ladles which lock onto and track the molds through the pouring zone. Each ladle holds sufficient iron to pour a single mold. More specifically, a plurality of pouring ladles are each mounted on a separate, independently driven and controlled carriage which moves unidirectionally on a track in a closed loop between: (1) a ladle-filling station beneath the holding vessel; (2) a pouring station where the ladle locks onto, tracks and pours an associated mold as the ladle and mold move together through the pouring station; and (3) then back to the filling station. Each ladle carriage is controlled by its interaction with preceding and succeeding carriages in the system. In the pouring zone, the ladle carriage is mechanically coupled to a mold to be poured to maintain the ladle's pouring spout in registry with the pouring basin of the moving mold. Once coupled, the mold line drags the ladle through the pouring zone. After emptying its contents, the mechanical coupling device is disengaged, and the ladle then driven under its own power back to the filling station for refilling and repeat of the cycle. In each case, the molten iron falls through air from the holding vessel into the ladle, splashes as it enters the ladle, is thereafter agitated as the ladle moves from the filling station to the pouring zone and finally falls through air from the ladle into the mold.
While such equipment is suitable for pouring iron, it is not suitable for pouring molten aluminum which is highly reactive with air (i.e. O.sub.2, H.sub.2 O, CO.sub.2, and CO) and susceptible to hydrogen pickup from the H.sub.2 O. Aluminum reacts with oxygen to form a surface film of Al.sub.2 O.sub.3 which slows further oxidation. Such free-falling, splashing and agitation of the aluminum breaks this surface film and exposes unoxidized aluminum to the air which in turn causes entrapment of Al.sub.2 O.sub.3 films in the aluminum and/or reaction with ambient gases and consequent formation of Al.sub.2 O.sub.3, and dissolution of excessive amounts of hydrogen in the aluminum. Turbulence during the transfer of aluminum causes Al.sub.2 O.sub.3 to pile up, forming dross which tends to stick to vessel walls and sporadically slough inclusions into the molten aluminum. The presence of Al.sub.2 O.sub.3 and/or dissolved gas in the aluminum results in the formation of inclusions and gas bubbles in the casting. Moreover, the dissolved hydrogen tends to come out of solution and form hydrogen bubbles particularly easily in aluminum during the slow cooling thereof which is characteristic of sand casting processes. Both the gas bubbles and the inclusions are detrimental to the aluminum casting.
It is desirable for economic reasons to gravity cast substantially inclusion-free, gas-free aluminum into sand molds, and it would be desirable to devise an automatic pouring machine therefor which does not result in castings having gas bubbles or inclusions trapped therein.
Accordingly, it is the principal object of the present invention to provide a machine for automatically, gravity pouring any metal, and particularly for pouring substantially gas-free, inclusion-free aluminum, into a series of continuously moving sand molds. This and other objects and advantages of the present invention will become more readily apparent from the detailed description thereof which follows.